Influence of antifoams on efficiency and toxicity in cellulases production by Trichoderma reesei

Biofuels is a promising alternative to fossil fuels and many researches are nowadays focused on second-generation bioethanol. To achieve the production of 2G bioethanol, lignocellulosic biomass is first pretreated to improve the enzymatic hydrolysis of the cellulosic fraction before the alcoholic fermentation. The required enzymes for the hydrolysis step are produced by microorganisms, especially filamentous fungi such as Trichoderma reesei. Nevertheless, this fungus secretes not only the desired cellulases but also a huge number of other proteins, including hydrophobins. Hydrophobins are responsible for the foaming occurring during the aerobic and stirred fermentations. This foaming issue leads to use antifoams and to keep a safety volume.

The aim of this work is to study the effect of different kinds of antifoams during Trichoderma reesei fermentations. Foaming tests were developed by using real media (filtrates from fermentation broths). A protocol was developed to make foam by using a stirrer and a glass vessel to measure the amount of foam. Antifoam efficiency was measured by the time required for the foam clearing once antifoam was added to the foaming medium. Moreover, despite of antifoams influence on dissolved oxygen, some k_L.a measures were performed on filtrated broths containing different antifoams and at different air flows and stirring rates. Finally, Trichoderma reesei fermentations were carried out by using selected antifoams to evaluate their toxicity and their impact on the fungus metabolism, especially the effect on the proteins production.